Groovy-ism Rules ("rulesets/groovyism.xml")

These are rules covering Groovy idiomatic usage, and Groovy-specific bad practices.

AssignCollectionSort Rule

Since CodeNarc 0.15

The Collections.sort() method mutates the list and returns the list as a value. If you are assigning the result of sort() to a variable, then you probably don't realize that you're also modifying the original list as well. This is frequently the cause of subtle bugs. This violation is triggered when a sort() method call appears as the right hand side of an assignment, or when it appears as the first method call in a series of chained method calls.

Example of violations:

  def a = myList.sort()
  def b = myList.sort() { it }
  def c = myList.sort().findAll { x < 1 }

AssignCollectionUnique Rule

Since CodeNarc 0.15

The Collections.unique() method mutates the list and returns the list as a value. If you are assigning the result of unique() to a variable, then you probably don't realize that you're also modifying the original list as well. This is frequently the cause of subtle bugs. This violation is triggered when a unique() method call appears as the right hand side of an assignment, or when it appears as the first method call in a series of chained method calls.

Example of violations:

  def a = myList.unique()
  def b = myList.unique() { it }
  def c = myList.unique().findAll { x < 1 }

ClosureAsLastMethodParameter Rule

Since CodeNarc 0.14

If a method is called and the last parameter is an inline closure then it can be declared outside of the method call parentheses.

Example of violations:

    // creates violation: poor Groovy style
    [1,2,3].each({ println it })

    // no violation
    [1,2,3].each { println it }

CollectAllIsDeprecated Rule

Since CodeNarc 0.16

The collectAll method is deprecated since Groovy 1.8.1. Use collectNested instead.

Example of violations:

def list = [1, 2, [3, 4, [5, 6]], 7]

list.collectAll { it * 2 }      // deprecated

list.collectNested { it * 2 }   // replacement

ConfusingMultipleReturns Rule

Since CodeNarc 0.16

Multiple return values can be used to set several variables at once. To use multiple return values, the left hand side of the assignment must be enclosed in parenthesis. If not, then you are not using multiple return values, you're only assigning the last element.

Example of violations:

def a, b = [1, 2] // bad, b is null
def c, d, e = [1, 2, 3] // bad, c and d are null
class MyClass {
    def a, b, c = [1, 2, 3]  // bad, a and b are null
}

def x = 1              // ok
def (f, g) = [1, 2]    // ok
(a, b, c) = [1, 2, 3]  // ok

ExplicitArrayListInstantiation Rule

Since CodeNarc 0.11

This rule checks for explicit calls to the no-argument constructor of ArrayList. In Groovy, it is best to write new ArrayList() as [], which creates the same object.

ExplicitCallToAndMethod Rule

Since CodeNarc 0.11

This rule detects when the and(Object) method is called directly in code instead of using the & operator. A groovier way to express this: a.and(b) is this: a & b. This rule can be configured to ignore this.and(Object) using the ignoreThisReference property. It defaults to true, so even and(x) will not trigger a violation. The default is true because and appears commonly in Grails criteria.

This rule also ignores all calls to super.and(Object).

ExplicitCallToCompareToMethod Rule

Since CodeNarc 0.11

This rule detects when the compareTo(Object) method is called directly in code instead of using the <=>, >, >=, <, and <= operators. A groovier way to express this: a.compareTo(b) is this: a <=> b, or using the other operators. Here are some other ways to write groovier code:

    a.compareTo(b) == 0               // can be replaced by: a == b
    a.compareTo(b)                    // can be replaced by: a <=> b
    a.compareTo(b) > 0                // can be replaced by: a > b
    a.compareTo(b) >= 0               // can be replaced by: a >= b
    a.compareTo(b) < 0                // can be replaced by: a < b
    a.compareTo(b) <= 0               // can be replaced by: a <= b

This rule can be configured to ignore this.compareTo(Object) using the ignoreThisReference property. It defaults to false, so even compareTo(x) will trigger a violation.

This rule also ignores all calls to super.compareTo(Object).

ExplicitCallToDivMethod Rule

Since CodeNarc 0.11

This rule detects when the div(Object) method is called directly in code instead of using the / operator. A groovier way to express this: a.div(b) is this: a / b. This rule can be configured to ignore div.xor(Object) using the ignoreThisReference property. It defaults to false, so even div(x) will trigger a violation.

This rule also ignores all calls to super.div(Object).

ExplicitCallToEqualsMethod Rule

Since CodeNarc 0.11

This rule detects when the equals(Object) method is called directly in code instead of using the == or != operator. A groovier way to express this: a.equals(b) is this: a == b and a groovier way to express : !a.equals(b) is: a != b. This rule can be configured to ignore this.equals(Object) using the ignoreThisReference property. It defaults to false, so even equals(x) will trigger a violation.

This rule also ignores all calls to super.equals(Object).

ExplicitCallToGetAtMethod Rule

Since CodeNarc 0.11

This rule detects when the getAt(Object) method is called directly in code instead of using the [] index operator. A groovier way to express this: a.getAt(b) is this: a[b]. This rule can be configured to ignore this.getAt(Object) using the ignoreThisReference property. It defaults to false, so even getAt(x) will trigger a violation.

This rule also ignores all calls to super.getAt(Object).

ExplicitCallToLeftShiftMethod Rule

Since CodeNarc 0.11

This rule detects when the leftShift(Object) method is called directly in code instead of using the << operator. A groovier way to express this: a.leftShift(b) is this: a << b. This rule can be configured to ignore this.leftShift(Object) using the ignoreThisReference property. It defaults to false, so even leftShift(x) will trigger a violation.

This rule also ignores all calls to super.leftShift(Object).

ExplicitCallToMinusMethod Rule

Since CodeNarc 0.11

This rule detects when the minus(Object) method is called directly in code instead of using the - operator. A groovier way to express this: a.minus(b) is this: a - b. This rule can be configured to ignore minus.xor(Object) using the ignoreThisReference property. It defaults to false, so even minus(x) will trigger a violation.

This rule also ignores all calls to super.minus(Object).

ExplicitCallToMultiplyMethod Rule

Since CodeNarc 0.11

This rule detects when the multiply(Object) method is called directly in code instead of using the * operator. A groovier way to express this: a.multiply(b) is this: a * b. This rule can be configured to ignore this.multiply(Object) using the ignoreThisReference property. It defaults to false, so even multiply(x) will trigger a violation.

This rule also ignores all calls to super.multiply(Object).

ExplicitCallToModMethod Rule

Since CodeNarc 0.11

This rule detects when the mod(Object) method is called directly in code instead of using the % operator. A groovier way to express this: a.mod(b) is this: a % b. This rule can be configured to ignore this.mod(Object) using the ignoreThisReference property. It defaults to false, so even mod(x) will trigger a violation.

This rule also ignores all calls to super.mod(Object).

ExplicitCallToOrMethod Rule

Since CodeNarc 0.11

This rule detects when the or(Object) method is called directly in code instead of using the | operator. A groovier way to express this: a.or(b) is this: a | b. This rule can be configured to ignore this.or(Object) using the ignoreThisReference property. It defaults to true, so even or(x) will not trigger a violation. This is the default because it is commonly used in Grails criteria.

This rule also ignores all calls to super.or(Object).

ExplicitCallToPlusMethod Rule

Since CodeNarc 0.11

This rule detects when the plus(Object) method is called directly in code instead of using the + operator. A groovier way to express this: a.plus(b) is this: a + b. This rule can be configured to ignore this.plus(Object) using the ignoreThisReference property. It defaults to false, so even plus(x) will trigger a violation.

This rule also ignores all calls to super.plus(Object).

ExplicitCallToPowerMethod Rule

Since CodeNarc 0.11

This rule detects when the power(Object) method is called directly in code instead of using the ** operator. A groovier way to express this: a.power(b) is this: a ** b. This rule can be configured to ignore this.power(Object) using the ignoreThisReference property. It defaults to false, so even power(x) will trigger a violation.

This rule also ignores all calls to super.power(Object).

ExplicitCallToRightShiftMethod Rule

Since CodeNarc 0.11

This rule detects when the rightShift(Object) method is called directly in code instead of using the >> operator. A groovier way to express this: a.rightShift(b) is this: a >> b. This rule can be configured to ignore this.rightShift(Object) using the ignoreThisReference property. It defaults to false, so even rightShift(x) will trigger a violation.

This rule also ignores all calls to super.rightShift(Object).

ExplicitCallToXorMethod Rule

Since CodeNarc 0.11

This rule detects when the xor(Object) method is called directly in code instead of using the ^ operator. A groovier way to express this: a.xor(b) is this: a ^ b. This rule can be configured to ignore this.xor(Object) using the ignoreThisReference property. It defaults to false, so even xor(x) will trigger a violation.

This rule also ignores all calls to super.xor(Object).

ExplicitHashMapInstantiation Rule

Since CodeNarc 0.11

This rule checks for explicit calls to the no-argument constructor of HashMap. In Groovy, it is best to replace new HashMap() with [:], which creates (mostly) the same object. [:] is technically a LinkedHashMap but it is very rare that someone absolutely needs an instance of HashMap and not a subclass.

ExplicitLinkedHashMapInstantiation Rule

Since in CodeNarc 0.14

This rule checks for the explicit instantiation of a LinkedHashMap using the no-arg constructor. In Groovy, it is best to replace new LinkedHashMap() with [:], which creates the same object.

ExplicitHashSetInstantiation Rule

Since CodeNarc 0.11

This rule checks for explicit calls to the no-argument constructor of HashSet. In Groovy, it is best to replace new HashSet() with [] as Set, which creates the same object.

ExplicitLinkedListInstantiation Rule

Since CodeNarc 0.11

This rule checks for explicit calls to the no-argument constructor of LinkedList. In Groovy, it is best to replace new LinkedList() with [] as Queue, which creates the same object.

ExplicitStackInstantiation Rule

Since CodeNarc 0.11

This rule checks for explicit calls to the no-argument constructor of Stack. In Groovy, it is best to replace new Stack() with [] as Stack, which creates the same object.

ExplicitTreeSetInstantiation Rule

Since CodeNarc 0.11

This rule checks for explicit calls to the no-argument constructor of TreeSet. In Groovy, it is best to replace new TreeSet() with [] as SortedSet, which creates the same object.

GetterMethodCouldBeProperty Rule

Since CodeNarc 0.16

If a class defines a public method that follows the Java getter notation and that returns a constant, then it is cleaner to provide a Groovy property for the value rather than a Groovy method.

Property Description Default Value
ignoreMethodsWithOverrideAnnotation If true, then do not check methods annotated with @Override. false

Example of violations:

    interface Parent {
        String getSomething()
        String getSomethingElse()
    }

    class Child extends Parent {
        static VALUE = 'value'

        @Override
        String getSomething() {
            'something'         // this could be simplified
        }

        @Override
        String getSomethingElse() {
            VALUE       // this could be simplified
        }

        int getOtherValue() {
            123
        }

        static String getName() {
            'MyName'
        }
    }

    class Child2 extends Parent {
        static VALUE = 'value'
        final String something = 'something'    // this is cleaner
        final String somethingElse = VALUE      // this is cleaner
        final int otherValue = 123              // this is cleaner
        static final String name = 'MyName'     // this is cleaner
    }

GroovyLangImmutable Rule

Since CodeNarc 0.13

The groovy.lang.Immutable annotation has been deprecated and replaced by groovy.transform.Immutable. Do not use the Immutable in groovy.lang.

Example of violations:

    @Immutable                          // Violation (no import means groovy.lang.Immutable)
    class Person { }

    @groovy.lang.Immutable              // Violation
    class Person { }

    import groovy.lang.Immutable as Imtl
    @Imtl                               // Violation
    class Person { }

Example of valid use of @Immutable:

    @groovy.transform.Immutable                 // OK
    class Person { }

    import groovy.transform.Immutable           // OK
    @Immutable
    class Person { }

    import groovy.transform.*
    @Immutable                                  // OK
    class Person { }

    import groovy.transform.Immutable as Imtl
    @Imtl                                       // OK
    class Person { }

    @javax.annotation.concurrent.Immutable      // OK
    class MyClass { }

GStringAsMapKey Rule

Since CodeNarc 0.11

A GString should not be used as a map key since its hashcode is not guaranteed to be stable. Consider calling key.toString().

Here is an example of code that produces a violation:

    Map map = ["${someRef}" : 'invalid' ]       // violation

GStringExpressionWithinString Rule

Since CodeNarc 0.19

Check for regular (single quote) strings containing a GString-type expression ($..).

Example of violations:

    def str1 = 'total: ${count}'                // violation
    def str2 = 'average: ${total / count}'      // violation

    def str3 = "abc ${count}"                   // ok; GString
    def str4 = '$123'                           // ok
    def str5 = 'abc {123}'                      // ok

UseCollectMany Rule

Since CodeNarc 0.16

In many case collectMany() yields the same result as collect.flatten(). It is easier to understand and more clearly conveys the intent.

Example of violations:

def l = [1, 2, 3, 4]

l.collect{ [it, it*2] }.flatten() // suboptimal

l.collectMany{ [it, it*2] }       // same functionality, better readability

UseCollectNested Rule

Since CodeNarc 0.16

Instead of nested collect calls use collectNested.

Example of violations:

def list = [1, 2, [3, 4, 5, 6], [7]]

println list.collect { elem ->
    if (elem instanceof List)
        elem.collect {it *2} // violation
    else elem * 2
}

println list.collect([8]) {
    if (it instanceof List)
        it.collect {it *2} // violation
    else it * 2
}

println list.collectNested { it * 2 } // same functionality, better readability